Enhancing thermophilic methane production from oil palm empty fruit bunches through various pretreatment methods: A comparative study

Abstract

This study investigated the effects of various pretreatment methods on the anaerobic digestibility of oil palm empty fruit bunches (EFB) for methane production. Pretreatment methods included weak alkaline (2 % Ca(OH)2), weak acid (2 % acetic acid), acidified palm oil mill effluent (POME), biogas effluent, hydrothermal (180 °C, 190 °C, and 200 °C), and microwave pretreatments. All pretreatment methods enhanced methane yield compared to untreated EFB (189.45 mL-CH4/g-VS), with weak alkaline pretreatment being the most effective (277.11 mL-CH4/g-VS), followed by hydrothermal pretreatment at 180 °C (244.33 mL-CH4/g-VS) and biogas effluent pretreatment (238.32 mL-CH4/g-VS). The enhanced methane yield was attributed to increased cellulose content (45.5 % for weak alkaline pretreatment), reduced hemicellulose (18.0 % for hydrothermal pretreatment at 200 °C), and lignin contents (19.0 % for hydrothermal pretreatment at 200 °C), decreased crystallinity index (40.0 % for hydrothermal pretreatment at 200 °C), and increased surface area. Weak alkaline pretreatment also showed the highest net energy balance (8.73 kJ/g-VS) and a short break-even point (2 years). Microbial community analysis revealed that weak alkaline pretreatment favored the growth of syntrophic acetate-oxidizing bacteria and hydrogenotrophic methanogens, contributing to improved methane yield. This study demonstrates the potential of EFB pretreatment, particularly weak alkaline and biogas effluent pretreatment, for enhancing methane production and sustainable management of palm oil mill waste.